1. Field of the Invention
The present invention relates to a method for drying the multi-layer paper insulation of high voltage electrotechnical equipments, such as transformer bushings, by means of microwaves. To carry out into practice the drying method, the present invention also relates to a microwave energy applicator as well as to a dryer apparatus including the latter applicator.
2. Brief Description of the Prior Art
In high voltage transformers, bushings traverse the metallic housing to permit connection with the winding terminals from the outside. Such a bushing comprises a through conductor wrapped in a multi-layer paper insulation. The paper insulation and a portion of the conductor are enclosed within a hermetically closed, cylindrical ceramic envelope filled with oil. The paper insulation is accordingly impregnated with this oil.
In use, humidity infiltrates within the bushing through fissures and joints in the ceramic envelope. Water therefore permeates the paper to destroy the dielectric insulation. The bushing must then be reconditioned.
To recondition the bushing, it is known to remove the through conductor with its paper insulation from the ceramic envelope, and to dispose these conductor and insulation in a conventional oven. The drawback of the conventional ovens is that the drying is very long, up to one month. Accordingly, such drying is so costly that the bushings are disposed of and replaced; replacement of the bushings being more advantageous than reconditioning them by drying of the paper insulation.